I don't use sponsorships.0014107 and 0012720 have been the last issues entered by a user related to this feature.
I opened 0017662 some while ago which has been closed by you as "won't fix"

I hardly get questions related to sponsorships in form.
It seems there are just very few users using (maybe just trying) this feature.

A clean removal of sponsorship would require a database schema change.
I would like us to have the same schema in 1.3.x and 2.0.x as it would be fine to be able to run 1.3 and 2.0 in parallel, connected to the same database.

The general problem is, that we hardly know what our users are doing.
What about asking them some questions in release announcement for 1.3.0?
Something like:
"
Our plan is to remove some MantisBT features to be able to concentrate on most used core features.
Which of the following features do you use?

As per the draft release notes for 1.3.0 we discussed last week, Sponsorship is noted as deprecated. I don't think it was listed as such before that, and furthermore this does not seem to be documented anywhere (e.g. admin guide, config_defaults_inc.php), which is something that needs to be done prior to releasing 1.3.0.

I don't use this feature myself.

I would like us to have the same schema in 1.3.x and 2.0.x

+1 to that.

But we can do the removal of sponsorship in 2 steps

code in 2.0.x

db schema in next feature release

What about asking them some questions in release announcement for 1.3.0?

That sounds great on paper, but to do this right we should really setup a proper survey (like rombert wanted to do several years ago, leading me to setup Limesurvey, but that never got anywhere)